In many industrial plants, such as refineries, a liquid is heated by flowing through a heat exchanger comprising a bundle of vertical or horizontal tubes over which pass the flue gases of a furnace. In some cases, the tubes are bare radiant tubes having smooth outer surfaces while in others each tube is a finned convention tube having closely spaced fins projecting from its outer surface to increase the surface area of the tube and thereby improve the heat transfer.
In use, because of incomplete combustion of the fuel burned in the furnace, a deposit of soot and other combustion products can form on the tubes, which causes serious deterioration in efficiency, if allowed to build up. To maintain good performance, it is therefore necessary to clean the tube bundles periodically.
It is known to clean furnace tube bundles by spraying them with a chemical. To enable a spray lance to be introduced between the tubes, the tubes of the bundle are arranged in a regular array, usually hexagonal, with a gap between the outer surfaces or the fins of adjacent tubes sufficiently wide to allow the spray lance to penetrate deep into the bundle.
Other on-line known ways of cleaning the outside of the tubes are to blow off the deposit with high pressure air using soot blower technology, to shock it off using fireball technology and on-line injection of abrasive blast and chemical media into the upward draft of the flame.
Offline cleaning technology may involve a person entering entry inside the furnace in order to apply high pressure water jets or other blast medium. All these systems have limited effectiveness as they cannot reach deep inside the furnace and in between fouled finned steel tubes which may be some 20 m long and comprises finned tubes of 15 cm diameter arranged six tubes deep in an array of triangular pitch formation.
A search carried out by the UK Patent Office revealed the existence of US published Patent Applications US2011/067651 and US2007/102902 and U.S. Pat. No. 6,513,462.